Trusted Cooperative Transmissions: Turning a Security Weakness into a Security Enhancement

Since the invention of wireless telegraphy, the effort to improve wireless channel capacity has never stopped. In the last decade, significant advancement has been made and this advancement has featured two milestones. The first milestone is

Multiple-Input-Multiple-Output (MIMO)

techniques, which create spatial diversity by taking advantage of multiple antennas and improvesthe wireless channel capacity by an amount on the order of the number of antennas on a wireless device. The second milestone is

cooperative transmission

. Instead of relying on the installation of multiple antennas on one wireless device, cooperative transmission achieves spatial diversity through physical layer cooperation. In cooperative transmission, when the source node transmits a message to the destination node, the nearby nodes that overhear this transmission will “help” the source and destination by relaying the replicas of the message, and the destination will combine the multiple received waveforms so as to improve the link quality. In other words, cooperative transmission techniques utilize nearby nodes as virtual antennas, and mimic the effects of MIMO in achieving spatial diversity.